Medical imaging often is conducted in tandem with the insertion of a needle, catheter, or other instrument into a subject in order to obtain a biopsy sample or perform an image-assisted medical procedure. For example, it has become increasingly accepted to perform standard radiography, fluoroscopy, ultrasound, computed tomography (CT) scanning, and magnetic resonance (MR) imaging while a medical instrument is being positioned and/or operated. In order for the imaging to be useful, it is important to provide a known alignment between the imager and medical instrument. Although it is possible to perform image-assisted medical procedures by positioning an instrument visually using an iterative process in which the instrument's trajectory is adjusted following inspection of successive images showing the instrument's position, such a technique is inefficient, slow, cumbersome and suffers from high risk associated with initial improper alignment.
For example, ultrasound is known to have use in real time needle guidance, enabling accurate targeting of internal structures during interventional procedures such as biopsy, drainage or focal therapies that can be delivered through a needle or small diameter probe. There are two fundamental techniques for ultrasound guided needle placement. One approach is known as the “freehand method,” in which an ultrasound imaging transducer and needle are not coupled and thus are independently movable throughout a procedure. In this method, the needle and path to a target organ are visualized by a skilled operator who holds the transducer in one hand while advancing the needle with the other. The coordination and visual and spatial orientation skills required to simultaneously maintain the image plane in line with the needle, keep the target in view, maintain orientation to surrounding structures and manipulate the needle are substantial and demanding. Thus, the technique is not suitable for, or favored by everyone, and there is a steep and prolonged learning curve. The main advantage of the freehand method is the complete versatility allowed by total freedom of movement of both needle and ultrasound imaging transducer.
An alternate approach is known as the “needle guide method,” in which a needle guide having a known orientation to the ultrasound imaging transducer is used. Such guides may be integral with the transducer, or instead may be separate, attachable accessories, and have been made as either reusable or single-use, sterile, disposable products. In the needle guide method, the guides are designed to keep any needle passing through them on a known path in the image plane, and thus avoid many of the difficulties inherent in the freehand technique. Typically, software is supplied by the ultrasound equipment manufacturer showing a virtual guide path and depth index on a real time image.
The needle guide method is less reliant on user intuition, skills and experience and has a shorter learning curve, but has several limitations that have hampered universal acceptance. First, the freehand method permits the operator to choose any size needle without restriction, whereas the needle guide method typically has required a close tolerance path for each size needle to work properly. Because of this requirement, manufacturers of prior art needle guides have devised methods that typically either require significant manipulation of the guide or multiple parts to permit a range of needle sizes to be accommodated within their guides.
Second, the freehand method permits the operator to have complete freedom of choice for entry site of the needle and angle of attack to the target, whereas the needle guide method is generally more restricting, with prior art devices typically offering only a single angle of attack in relation to the ultrasound transducer. To address this restriction, some re-usable needle guides have been designed to offer up to three different angles of attack, but such devices have required significant manual manipulation and have been considered cumbersome by some users.
Third, when using the needle guide method the needle often must be decoupled from the guide to continue some procedures, inevitably requiring additional and sometimes awkward, time consuming steps. On the other hand, the freehand method permits the operator complete freedom with the needle once it is in the desired location because the needle movement is not governed or otherwise restricted by a guide.
Fourth, the needle guide method introduces additional problems including: the requirement for a secure attachment to the transducer that does not interfere with transducer function, the possible requirement for added needle length (to allow for the length of the guide), and the issue of “dead space” that can exist between the exit of the needle tip from the guide and the entry into the skin which may contribute to misdirection of the needle. There also may be added costs to the user, although such costs may be balanced by the need for a less experienced operator and fewer complications for the patient.
To avoid some of the aforementioned disadvantages as described above, various devices are known for use in guiding medical instruments.
For example, U.S. Pat. No. 6,203,499 B1 to Imling et al. is directed to a multiple angle needle guide comprised of a body that has a slot positioned between opposing sides. The slot creates a triangular shaped gap between the opposing sides spanning a range of 45° for inclination of a needle. With this device, the angle of attack in the image plane is not fixed to a known previously determined path or paths, nor is the needle fully engaged in the guide but instead free floating in the slot. Also, the slot is not adjustable in width and therefore is only useful for a limited range of needle sizes.
U.S. Pat. No. 5,031,634 to Simon is directed to an adjustable biopsy needle-guide device that can be used to direct a variety of separate aspiration biopsy needles or tissue cutting biopsy needles to a target lesion. Sets of aligned holes are provided in a handle to aim and control the depth of the needles, with different hole sizes accommodating various needle gauges. In some applications, the required angle of insertion is guided by a goniometer or protractor, or the guide is supported by an adjustable stereotactic device attached to the patient's skin or a table top. The patent also states that if fluoroscopy is the selected imaging modality, a plastic side-arm attachment can be used to hold the handle of the device while it is being aimed or advanced into the tissues.
U.S. Pat. No. 5,052,396 to Wedel et al. is directed to a needle guide for ultrasound transducers having a means for coupling with a transducer and a multi-slotted, removable insert for receiving and guiding needles of various gauges. The configuration of the transducer, needle guide, needle, and the patient are such that a physician can firmly grasp the transducer and needle guide with one hand while maintaining contact with the patient, and manipulate the needle with the other hand.
In addition, U.S. Pat. No. 5,100,387 to Ng is directed to a disposable universal needle guide apparatus for amniocentesis. The needle guide apparatus includes a substantially horizontal base to be applied to a surface on or adjacent a zone to be punctured by a needle, an upright guide flange mounted on the base, and pivot structure associated with the flange and base. An elongated, tubular guide structure carried by the pivot structure is manually pivoted and receives the needle for guiding movement thereof at an angle determined by selective swinging of the tubular guide structure relative to the base.
Also, U.S. Pat. No. 5,941,889 to Cermak is directed to a multiple angle disposable needle guide system that includes a bracket, a mounting base, a pivoting portion of the mounting base, and a needle guide. The bracket is used to secure the needle guide system to an imaging instrument, such as an ultrasonic probe. The mounting base is secured to the imaging instrument by the bracket. The pivoting portion of the mounting base is configured to pivot along at least one axis, and the disposable needle guide is removably secured to the pivoting portion of the mounting base. The needle guide has a needle retainer member configured to retain a needle by application of a clamping force. A plurality of interchangeable needle retainer members are used so as to permit needles of various sizes to be used.
Despite these developments, there remains a need for an improved instrument guide that accommodates elongate instruments of different diameters without requiring cumbersome adjustments. There further remains a need for a guide that permits an instrument to be easily inserted and removed therefrom, particularly while the instrument (such as a needle or catheter) is in the patient. For example, it is known that with prior art instrument guides the instrument rotates or undergoes undesirable lateral movement during insertion and removal from a patient. Such lateral (sideways) movement preferably are minimized in order to avoid unnecessary patient discomfort and even trauma, while permitting axial movement into and out of the patient. Additionally, there remains a need for an instrument guide with a wide range of adjustment to accommodate different gauges of instruments.